Imaging optics with adjustable optical power and method of adjusting an optical power of an optics

ABSTRACT

The invention relates to optics comprising adjustable optical elements and, if desired, lenses of fixed focal lens. By use of an appropriate controller for the adjustable optical elements, characteristics of the optics can be advantageously varied. For this purpose, systems are provided which are suitable for use as surgical stereo-microscope, objective, ocular or zoom. A zoomable imaging optics comprises lenses and of variable optical power, which are oppositely controlled by means of a controller to change an imaging ratio, so that the optical power of the one lens is increased and the optical power of the other lens is decreased. Moreover, the imaging optics may comprise still further assemblies of fixed optical power.

This application is a divisional application and thus claims benefitpursuant to 35 U.S.C. §120, of U.S. patent application Ser. No.11/408,633 filed on Apr. 21, 2006, now U.S. Pat. No. 7,411,739, issuedAug. 12, 2008, which is a national stage application of PCT ApplicationNumber PCT/EP2004/012042, filed Oct. 25, 2004, which claims priorityfrom German Patent Application No. 103 49 293.3 filed on Oct. 23, 2003and German Patent Application No. 10 2004 026 580.1 filed on Jun. 1,2000.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates to imaging optics with adjustable optical power.The imaging optics is an optics of very general nature for use, forexample, in a camera, telescope, a microscope or other optics.Furthermore, the invention relates to a method of adjusting an opticalpower in particular of a zoomable imaging optics.

Furthermore, the invention relates to a stereo-microscopy system forgenerating a magnified stereoscopic image of an object, as well as to acorresponding stereo-microscopy method.

A zoomable imaging optics is an imaging optics, the imaging ratio ormagnification of which is variable.

2. Brief Description of Related Art

A conventional zoomable imaging optics comprises three lens assemblies,one of which is fixedly mounted in a support and the two other ones aredisplaceable along an optical axis of the optics to vary amagnification. In order to correctly displace these two lens assembliesrelative to one another and relative to the fixedly positioned lensassembly, quite complex mechanics are required. Moreover, the necessarydisplacement of the lens assemblies requires the optics to have arelatively large minimum overall length.

From U.S. Pat. No. 4,820,028 a zoomable optics is known comprising alens of variable optical power for changing the magnification, so that amechanical displacement of lenses along the optical axis is notnecessary. The lens of variable optical power forms part of an opticswhich, moreover, comprises plural lenses of fixed optical power andenables a relatively good compensation of imaging aberrations at aspecific setting of the lens of variable optical power. However, if theoptical power of the lens of variable optical power is varied to changethe magnification, imaging aberrations occur which have a disturbingeffect.

A conventional stereo-microscopy system comprises a left-hand stereooptics for generating a left-hand partial image of the stereoscopicimage, as well as a right-hand partial stereo optics for generating aright-hand partial image of the stereoscopic image.

U.S. Pat. No. 6,081,372, for example, discloses a stereo-microscopysystem of the so-called “Grenough” type, wherein each one of theleft-hand partial stereo optics and the right-hand partial stereo opticscomprises a separate objective assembly. Principal axes of both partialstereo optics are oriented at an angle relative to one another such thatthey intersect in an object plane of the two objective assemblies. If,in such a stereo-microscopy system, a working distance between theobject plane and the objective assemblies is to be changed, the anglebetween the two principal axes must be changed accordingly, whichrenders the required mechanics unreasonably complex under practicalaspects.

DE 90 16 892 U1 and U.S. Pat. No. 5,701,196 disclose stereo-microscopysystems, wherein an objective is provided for transforming anobject-side beam bundle, emanating from an object plane of theobjective, into an image-side beam bundle, and wherein left-hand partialstereo optics and right-hand partial stereo optics are provided in therespective image-side beam bundle and extract therefrom a left-handpartial beam bundle and a right-hand partial beam bundle, respectively,to generate therefrom the left-hand partial image and the right-handpartial image, respectively, of the stereoscopic image. The principalaxes of the two partial beam bundles of the left-hand and right-handpartial stereo optics are fixedly positioned spaced apart from anotherand traverse the common objective also spaced apart from each other. Theobjective provides an optical power of a round lens. The objectivecomprises at least one assembly of positive optical power and oneassembly of negative optical power, a distance between the twoassemblies being variable to change a working distance between theobjective and an object plane of the objective. In contrast to thestereo-microscopy system known from U.S. Pat. No. 6,081,372, no angleneed to be changed between the principal axes of the two partial stereooptics in order to change a working distance.

The stereo-microscopy systems known from DE 90 16 892 U1 and U.S. Pat.No. 5,701,196 have proved successful in practice as far as the change ofthe working distance is concerned, but exhibit different opticalcharacteristics, as against a comparable stereo-microscope with fixedworking distance, i.e., wherein the working distance is not changeable.For example, in the stereo-microscopy system known from DE 90 16 892 U1,the assembly having a negative optical power is disposed closer to theobject plane than the assembly having a positive optical power.Consequently, a principal plane of the objective is disposed, viewedfrom the object plane of the objective, behind the objective.Accordingly, a focal length of the objective is longer than a workingdistance between objective and objective plane. Due to the, as comparedto the working distance, long focal length, the objective exhibits atotal magnification, stereo impression and resolution which arediminished as compared to the corresponding objective with fixed focallength in which the focal length corresponds about to the workingdistance.

In the stereo-microscopy system known from U.S. Pat. No. 5,701,196, theassembly of positive optical power is disposed closer to the objectplane than the lens assembly of negative optical power. As a result, aprincipal axis of the objective is disposed between the objective andthe object plane. Accordingly, a focal length of the objective isshorter than a working distance between the object plane and theobjective as such. This causes a decrease in the object field diameterand the depth of field as well as in an increase in the overall length,the overall volume and weight as compared to a corresponding objectivewith fixed focal length.

SUMMARY OF THE INVENTION

The present invention has been accomplished taking the above problemsinto consideration.

It is an object of the present invention to provide a zoomable imagingoptics, wherein the required optical imaging quality is appropriatelyachieved by use of a lens of variable optical power.

Furthermore, it is an object of the invention to provide a method ofcontrolling an imaging optics with variable magnification.

Furthermore, it is an object of the invention to provide imaging opticswhich can be easily equipped with a zoom function.

A further object of the present invention is to provide astereo-microscopy system with variable optical properties, such as avariable working distance, which stereo-microscopy system is comparable,as far as its optical qualities and/or its overall volume and weight areconcerned, with a corresponding microscopy system with fixed workingdistance.

According to one aspect of the invention, a zoomable imaging optics isprovided which comprises at least two lenses of variable optical powerdisposed spaced apart from one another along a common optical axis. Inorder to change the imaging ratio and magnification, respectively,provided by the imaging optics, the two lenses of variable optical powerare controlled oppositely, i.e., in counter direction, that is, a firstone of the two lenses is controlled to increase the optical powerprovided by said lens, while a second one of the two lenses of variableoptical power is controlled to decrease the optical power provided bythe same, and vice versa.

The zoomable imaging optics may constitute a part of a larger opticalsystem which, moreover, comprises, for example, an ocular or/and imagedetector or/and an objective and other optical components.

According to an exemplary embodiment, the zoomable imaging opticscomprises merely the two lenses of variable optical power and no furtherlenses of fixed optical power.

According to a further exemplary embodiment, the zoomable imaging opticscomprises at least one further lens of fixed optical power. According tothis exemplary embodiment, the lens of fixed optical power is notdisposed between the two lenses of variable optical power. According toan alternative exemplary embodiment, the at least one lens of fixedoptical power is disposed between the two lenses of variable opticalpower.

An optical axis is assignable to each one of the lenses of variableoptical power, so that the action of the lens of variable optical poweris that of a round lens so that, moreover, a focal length is assignableto this round lens action, said focal length being variable by varyingthe optical power of the lens. However, this does not exclude that thelens also provides a variable optical power which is not rotationallysymmetric in respect of the optical axis. Moreover, this does notexclude either that the lens of variable optical power is controllablesuch that the optical axis, to which the round lens action isassignable, is variable in respect of its spatial position, for example,as far as its orientation or a lateral displacement are concerned.

Due to the two lenses of variable optical power being oppositelycontrolled, a desired zoom effect is achievable, that is, a change inthe imaging ratio. Moreover, the opposite control causes at least apartial compensation of image aberrations. An example for this is achromatic aberration.

According to an exemplary embodiment, the zoomable imaging opticscomprises at least a partial imaging optics with at least one lens offixed optical power which may be selectively disposed in and removedfrom one of the beam paths traversing the two lenses of variable opticalpower. This allows to enlarge a range in which the imaging ratio of theimaging optics is variable. By correspondingly controlling the lenses ofvariable optical power, it is possible to change substantiallycontinuously the imaging ratio over a specific range. By positioning thepartial imaging optics in the beam path and by removing the same fromthe beam path, respectively, it is then possible, in addition, tostepwise increase and decrease the imaging ratio, respectively.According to an exemplary embodiment, the removal and insertion,respectively, of the partial imaging optics enables the imaging ratio tobe changed by at least 30%.

According to a further exemplary embodiment, the partial imaging opticsitself exhibits a telescopic construction, for example, that of aGalilean telescope or Keplerian telescope.

According to an exemplary embodiment, in order to fold the beam path, atleast one mirror is disposed in the beam path between the two lenses ofvariable optical power. This enables to realize zoomable imaging opticswhich exhibit a particularly short overall length. As the zoomableimaging optics includes no optical components which are displaceablealong the optical axis, an optical path length between successivefoldings of the beam path may be particularly short and, by pluralfolding of the beam path, a particularly compact zoomable imaging opticsis achievable.

According to a further aspect of the invention, a family of imagingoptics is provided, comprising at least two imaging optics, one of whichdoes not comprise lenses of variable optical power, the other onecomprising at least two lenses of variable optical power disposed spacedapart from one another in the beam path. These second imaging optics isthus zoomable by controlling the lenses of variable optical power. Thetwo imaging optics have specific features in common, such as, forexample, geometric properties. This includes, for example, the radii ofcurvature and diameter of the lens surfaces and vertex distances of thelens surfaces. This allows to cost-efficiently provide a product familyof optical devices which include common optical components so that themanufacture of these optical components and the assembly of the devicesis rendered cost-efficiently as well. One member of the family thenexhibits the zoom function due to the lenses of variable optical power,while another member of the family does not exhibit this property, butis available at lower cost.

This aspect of the invention is based on the finding of the inventorsthat even existing designs of imaging optics may offer a direct basisfor a design of an imaging optics which is rendered zoomable by twolenses of variable optical power. In this respect, an existing design ofan imaging optics can be taken as a basis which is supplemented in thattwo lenses of variable optical power are inserted spaced apart from eachother into this existing design. If these two lenses of variable opticalpower are then oppositely controlled, a change in the imaging ratioprovided by the optics is achieved.

According to a further aspect of the invention, a microscope withvariable magnification is provided, comprising an objective fortransforming an object-side beam bundle, emanating from an object planeof the objective, into an image-side beam bundle, and an image-formingassembly. The image-forming assembly may be, for example, an ocularthrough which the operator of the microscope views in order to directlyobserve optically an object disposed in the object plane. Theimage-forming assembly may also comprise an image detector, such as acamera, for taking an electronic image of the object.

Two lenses of variable optical power are disposed in an imaging beampath of the microscope between the object plane and the image-formingassembly, said lenses being oppositely controllable for varying theimaging ratio of the microscope, as explained above.

According to an exemplary embodiment, the two lenses of variable opticalpower are disposed in the objective.

According to a further exemplary embodiment, the two lenses of variableoptical power are disposed in the beam path between the objective andthe image-forming assembly.

According to a further exemplary embodiment, an optical assembly isprovided which is selectively insertable in and removable from the beampath in order to change the imaging ratio stepwise.

According to an exemplary embodiment, the partial optics is pivotableabout an axis which is oriented transversely to a direction of the beampath in order to move the partial optics into or out of the beam path.

According to a first aspect of the invention, a stereo-microscopy systemis provided, comprising a left-hand partial stereo optics and aright-hand partial stereo optics for generating a left-hand partialimage and a right-hand partial image, respectively, of the stereoscopicimage. The stereo-microscopy system, moreover, comprises an objectivecommonly traversed by the left-hand and right-hand partial beam bundlesof the left-hand partial stereo optics and the right-hand partial stereooptics, respectively.

The objective comprises a lens assembly of a first lens of positiveoptical power and a second lens of negative optical power, the indicesof refraction of the lens materials of the two lenses being differentfrom each other in order to achieve a correction of specificaberrations, such as, chromatic longitudinal aberrations and sphericalaberrations. To this end, the lens assembly can be in the form of acemented element.

The lens assembly, furthermore, comprises a third lens of variableoptical power. The first, second and third lenses are disposed spacedapart from one another along the optical axis at fixed distances fromone another. A focal length of the first lens and the second lenstogether, that is, without the third lens or, in the case that the thirdlens as such does not provide any optical power, is in a range between150 mm and 450 mm. The optical power of the third lens is variable suchthat a working distance between the object plane of the objective andone of the first, second or third lenses of the objective is variable atleast in a range of from 200 mm to 400 mm.

This allows to vary the working distance of the stereo-microscopysystem, without having to displace lenses of the objective relative toone another along the optical axis of the objective.

Lenses with adjustable and variable optical power are known per se fromthe prior art, for example, from U.S. Pat. No. 4,795,248 or U.S. Pat.No. 5,815,233. Such lenses of adjustable optical power comprise a liquidcrystal layer which is controllable via an electrode structure in orderto selectively adjust an optical path length through the liquid crystallayer for a beam traversing said layer spatially dependently, that is,via a cross-section of the lens. As a result, a flexible lens action isprovided. However, so far, it has not been achieved to successfullyintegrate such flexible lenses of adjustable optical power into astereo-microscopy system. According to the configuration provided by theinvention, however, a stereo-microscopy system with an objective isprovided having a working distance which is substantially equal to thefocal length of the objective.

Accordingly, the disadvantages described above in respect of theobjectives, wherein the working distance differs considerably from thefocal length, are reduced and advantageous properties regarding, forexample, total magnification, stereo impression, resolution, overalllength and weight, are achieved.

According to a further aspect of the invention, a stereo-microscopysystem is provided which, again, comprises a left-hand partial stereooptics and a right-hand partial stereo optics and a common objective.Each one of the two partial stereo optics comprises a zoom optics. Thetwo zoom optics are preferably of identical structure. However, thestructure of the zoom optics of the left-hand partial stereo optics maydiffer from the structure of the zoom optics of the right-hand partialstereo optics. However, the structure of the two zoom optics are similarin functional respect in that each one comprises two lens assembliesdisposed spaced apart from one another. Each one of the two lensassemblies comprises a first lens of positive optical power and a secondlens of negative optical power, as well as a third lens of adjustableoptical power. The first, second and third lenses of each lens assemblyare fixedly disposed relative to one another along a principal axis ofthe zoom optics, and the two lens assemblies are disposed spaced apartfrom each other by a fixed distance along the principal axis as well.This configuration enables to provide a variable magnification of thestereo-microscopy system, without having to displace lens assemblies ofthe zoom optics along the principal axis of the zoom optics, as it wasso far usual in prior art.

According to one embodiment, the third lens of the one lens assembly iscontrolled to increase the optical power of said lens, and the thirdlens of the other lens assembly is controlled to decrease the opticalpower of said lens in order to change the magnification provided by thezoom optics.

According to a further embodiment, a stereo-microscopy system isprovided comprising a left-hand partial stereo optics and a right-handpartial stereo optics. Each one of the left-hand and right-hand partialstereo optics comprises an ocular with a first lens of positive opticalpower, a second lens of negative optical power and a third lens ofvariable optical power, the distances between said lenses along anoptical axis of the ocular being fixed. The optical power of the thirdlens is adjustable in order to compensate defects of the eye of theoperator of the stereo-microscopy system who views through the ocular.This allows to compensate vision defects of the eye viewing through theocular, without components of the ocular or the ocular as a whole havingto be displaced. In particular, the third lens of adjustable opticalpower may provide a cylinder action, so that a simple way is achieved aswell of compensating an astigmatism of the eye viewing through theocular.

According to one embodiment, a controller for controlling the third lenscomprises a memory for storing values representative of the visiondefects of the eyes of different users. The oculars of thestereo-microscopy system are then selectively controlled to compensatefor the vision defects of one or more users. Preferably, the controllercomprises a user interface which allows the respective user to selectthe ocular setting allocated to the respective user and to changesettings in order to compensate his vision defects. The user interfacemay be in the form of a keyboard, a selection switch, a language controlor the like.

According to a further embodiment, a stereo-microscopy system isprovided, comprising a left-hand partial stereo optics and a right-handstereo optics, each one of the two partial stereo optics comprising aseparate objective. A working distance between the objectives and theobject planes thereof is variable, and at least one of the twoobjectives comprises a wedge prism exhibiting an adjustable wedge prismaction so that, even if the working distances are changed, precisestereoscopic partial images can be obtained via the left-hand andright-hand partial stereo optics, without principal axes of the partialstereo optics having to be mechanically changed as far as theirorientation relative to one another is concerned.

According to a further embodiment, a stereo-microscopy system isprovided, comprising a left-hand partial stereo optics and a right-handpartial stereo optics and a common objective. The common objectiveincludes a lens of positive optical power and an optical assembly whoseoptical path length provided for the beams traversing said assembly isvariable spatially dependently such that on each of the principal axesof the left-hand and right-hand partial stereo optics a round lensaction is provided. This assembly of the objective thus provides forboth partial stereo optics separate optical effects, so that saidassembly of the objective may provide functions which are conventionallyprovided by the two partial stereo optics themselves.

In this respect, it is in particular possible to displace in simplemanner the round lens action provided for the two partial stereo opticsin circumferential direction about a principal axis of the objective.Accordingly, as compared to conventional solutions, the number ofcomponents of the partial stereo optics which must be displaced when thepartial stereo optics are rotated in circumferential direction about theprincipal axis of the objective is reduced.

In particular, it is then also possible to provide simplified zoomsystems in the partial stereo optics in that, when a magnificationprovided by the zoom systems is changed, the intensity of the round lensaction can be changed as well.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing as well as other advantageous features of the inventionwill be more apparent from the following detailed description ofexemplary embodiments of the invention with reference to theaccompanying drawings. It is noted that not all possible embodiments ofthe present invention necessarily exhibit each and every, or any, of theadvantages identified herein.

FIG. 1 shows a cross-section through a lens of variable optical powerfor use in embodiments of the invention,

FIG. 2 is a detailed top-plan view of the lens of variable optical powershown in FIG. 1,

FIG. 3 shows a cross-section of a lens of variable optical power for usein embodiments of the invention,

FIG. 4 shows a stereo-microscopy system as an example of a total opticswhich may comprise a zoomable imaging optics according to the invention,

FIG. 5 shows an embodiment of a zoomable imaging optics comprising onlytwo lenses of variable optical power,

FIG. 6 shows a further embodiment of a zoomable imaging optics having astructure of a Galilean telescope,

FIG. 7 shows a further embodiment of a zoomable imaging optics havingthe structure of a Galilean telescope,

FIG. 8 shows a further embodiment of a zoomable imaging system havingthe structure of a Keplerian telescope,

FIG. 9 shows a further embodiment of a zoomable imaging optics in theform of a microscope objective,

FIG. 10 shows a further embodiment of a zoomable imaging optics withexchangeable partial optics, and

FIG. 11 shows a further embodiment of a zoomable imaging system with twolenses of variable optical power and a folded beam path therebetween,

FIG. 12 shows a cross-section through a lens group of variable opticalpower for use in embodiments of the invention,

FIG. 13 shows an embodiment of a zoomable imaging system of the Galileantype with two lens groups of variable optical power,

FIG. 14 shows an embodiment of a zoomable imaging system of theKeplerian type with two lens groups of variable optical power,

FIG. 15 shows a stereo-microscopy system including a common objective ofvariable focal length for two stereo beam paths,

FIG. 15 a to FIG. 15 c are partial views of the objective of thestereo-microscopy system of FIG. 15 in different settings,

FIG. 16 a to FIG. 16 c are partial views of a variant of thestereo-microscopy system of FIG. 4 with a zoom system of variablemagnification,

FIG. 17 a to FIG. 17 c are partial views of a further variant of thestereo-microscopy system of FIG. 4 with oculars for compensatingdifferent vision defects of the users,

FIG. 18 shows a further variant of the stereo-microscopy system shown inFIG. 15,

FIG. 19 shows an embodiment of a stereo-microscopy system with separateobjectives for the two stereo beam paths and variable working distance,and

FIG. 20 a to FIG. 20 c show a further embodiment of a zoom system indifferent settings.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the exemplary embodiments described below, components that are alikein function and structure are designated as far as possible by alikereference numerals. Therefore, to understand the features of theindividual components of a specific embodiment, the descriptions ofother embodiments and of the summary of the invention should be referredto.

Embodiments of the imaging optics according to the invention will now bedescribed in further detail which include lenses of variable opticalpower. First of all, an embodiment of such a lens of variable opticalpower will be described below with reference to FIGS. 1 and 2. Suchlenses are known, for example, from U.S. Pat. No. 4,795,248, U.S. Pat.No. 6,317,190 B1, U.S. Pat. No. 5,617,109, U.S. Pat. No. 4,909,626, U.S.Pat. No. 4,781,440, U.S. Pat. No. 4,190,330, U.S. Pat. No. 4,572,616 andU.S. Pat. No. 5,815,233, the full disclosures of which are incorporatedherein by reference.

FIG. 1 shows a cross-section through a lens 1 of variable optical power.Lens 1 comprises a first liquid crystal layer 3 and a second liquidcrystal layer 5, each being provided on one side of a common transparentcontinuous electrode 7. A further transparent electrode structure 9, asshown in plan view in FIG. 2, is disposed on a side of the liquidcrystal layer 3 opposite to the common electrode 7. The electrodestructure 9 provides a plurality of controllable pixels 11 which arearranged in a rectangular grid. A controller 13 is provided to apply anadjustable voltage to each pixel 11 via a driver 15 which supplies thevoltage to the individual pixels, as it is commonly known for liquidcrystal displays. Accordingly, an electrical field between a respectivepixel 11 and the common electrode is adjustable and, depending on howthe electric field is set, the liquid crystal layer 3 provides avariable optical path length for a light beam to traverse said liquidcrystal layer in a polarization direction of the beam 17. A furthertransparent electrode structure 9, configured as shown in FIG. 2, isdisposed on a side of the liquid crystal layer 5 facing away from thecommon electrode 7, said electrode structure 9 being likewise controlledby the controller 13. While the liquid crystal layer 3 provides thevariable optical path length in a polarization direction in the plane ofFIG. 1, as intimated by an arrow 19, the liquid crystal layer 5 providesa corresponding variable optical path length in a polarization directionorthogonal to the aforesaid polarization direction, as indicated bysymbol 21 in FIG. 1.

By appropriately controlling the electrode structure 9, it is thuspossible to provide for both polarization directions of the beam 17optical path lengths of the two liquid crystal layers 3, 5, said pathlengths being adjustable as a function of a position on the layers 3, 5.Accordingly, lens 1 as a whole can be controlled to provide adjustableoptical effects for the beam 17, such as a round lens action of positiveoptical power or negative optical power in respect of a selectableoptical axis, a cylinder lens action of positive optical power ornegative optical power in respect of an adjustable plane of symmetry, awedge prism action of adjustable power, but also actions whichcorrespond to more complex optical elements.

FIG. 3 shows a cross-section through a further lens 1 of variableoptical power. Lens 1 comprises a housing 21 with two entrance and exitwindows 23, respectively, which enclose two liquids 25 and 27 which havea different index of refraction and, preferably, are substantially notmiscible with each other. One of the liquids 25 is, for example, wateror an aqueous saline solution. The other liquid 27 is, for example, anoil. The housing 22 provides a conical wall 31 for the two liquids 25,27 which is symmetrical in respect of an optical axis 29 of the assemblyand which contacts an interface 33 between the two liquids at an angleof contact θ. A likewise conical electrode 35 is disposed within thewall 31, and an annular electrode 36 is disposed in the volume of liquid25 near the window 23. The liquid 25 is electrically conducting, whileliquid 27 is substantially electrically non-conducting. A voltagebetween the electrodes 35 and 36 is adjustable by a controller 13. Achange in the voltage between the electrodes 35 and 36 changes the angleθ which the interface 33 between the two liquids 25, 27 encloses withthe wall 31. By varying the voltage between the electrodes 35, 36, it isthus possible to change the shape and curvature of the interface 33, asit is schematically represented by the dashed line 33′ in FIG. 3. Due tothe different indices of refraction of the two liquids 25, 27, a lensaction which lens 1 imparts on a beam traversing said lens along theoptical axis 29 is variable.

A lens of the type shown in FIG. 3 can be obtained, for example, fromthe company Varioptic, 69007 Lyon, France.

Further lenses of variable optical power, which make use of a change inthe shape of an interface for varying the optical power, are known fromU.S. Pat. No. 6,369,954, CA 2,368,553 and U.S. Pat. No. 4,783,155, thefull disclosures of which are incorporated herein by reference.

The principles of the present invention are applicable to arbitraryimaging optics, such as, for example, film cameras, photo cameras,telescopes, measuring optics or microscopes. As an example, astereo-microscope will be described hereinbelow.

FIG. 4 schematically shows a conventional stereo-microscopy system 41,comprising an objective 43 for transforming an object-side beam bundle47, emanating from an object plane 45, into an image-side beam bundle49. The stereo-microscopy system 41 further comprises a left-handpartial optics 51 and a right-hand partial optics 51′, each of whichextracts a partial beam bundle 53 and 53′, respectively, from theimage-side beam bundle 49 and feeds the same to oculars 55 and 55′,respectively, as image-forming assemblies of the stereo-microscopysystem 41. To this end, each one of the left-hand and the right-handpartial stereo optics 51, 51′ comprises a zoom system 57 and 57′,respectively, consisting of plural lens groups 58, 58′, a tube with lensassemblies 59, 59′ and reflecting prisms 61, 61′, the beam path foldedby the reflecting prisms 61, 61′ being shown unfolded in FIG. 4.

The objective 43 comprises a lens assembly 63 of a lens 64 of negativeoptical power, said lens being the lens of the objective 43 which facesthe object plane 45. Furthermore, the lens assembly 63 comprises a lens65 of positive optical power which is cemented with the lens 64.

FIG. 5 shows an example of a zoomable imaging optics 57 a consistingmerely of two lenses 1 a ₁ and 1 a ₂ of variable optical power which aredisposed along a common optical axis spaced apart from one another by adistance d=28.8 mm. Each one of the two lenses 1 a ₁, 1 a ₂ of variableoptical power is of the type as described with reference to FIG. 3, thatis, each one of the two lenses 1 a ₁ and 1 a ₂ comprises an interface 33a between two liquids 25 a and 27 a which have different indices ofrefraction and are enclosed in a space between windows 23 a. Acontroller 13 a is provided to appropriately apply control voltages tothe lenses 1 a ₁ and 1 a ₂ for adjusting a radius of curvature of theinterfaces 33 a.

The following Table 1 indicates three settings of the lenses 1 a ₁ and 1a ₂ with focal lengths f₁ and f₂ caused by the controller 13 a.

TABLE 1 Lens 1a₁ Lens 1a₂ Setting No. Magnification 1/f₁ [dptr] 1/f₂[dptr] 1 1.0 0 0 2 1.25 6.5 −8.1 3 0.80 −8.1 6.5

The setting No. 3 is shown in FIG. 5, the beams passing through lenses 1a ₁ and 1 a ₂ being designated by reference number 103.

This imaging optics thus operates like a Galilean telescope and has anafocal beam path on the entrance and exit sides. Both lenses 1 a ₁ and 1a ₂ are oppositely controlled by the controller 13 a, that is,proceeding from a magnification of 1.0× at which both lenses have anoptical power of 0 dptr, the optical power of lens 1 a ₁ is increasedand the optical power of lens 1 a ₂ is decreased in order to increasethe magnification.

The curvature of the interface 33 a between the two media 25 a and 27 acauses, apart from the optical power indicated in Table 1 which isindicated for a wave length of 546 nm in dptr, also a chromaticlongitudinal aberration which is not negligible and is indicated in thefollowing Table 2 in dptr (dioptre) for each one of the lenses 1 a ₁ and1 a ₂ and for the total imaging optics 57 a as optical power differencebetween blue light at 480 nm and red light at 644 nm:

TABLE 2 Setting Lens Lens No. Magnification 1a₁ 1a₂ Total optics 57a 11.0 0 0 0 2 1.25 −0.3 0.3 −0.07 3 0.80 0.2 −0.2 −0.04

It is evident from Table 2 that each one of the lenses 1 a ₁ and 1 a ₂causes a considerable chromatic longitudinal aberration, but that thechromatic longitudinal aberration of the total optics 57 a isconsiderably smaller than the chromatic longitudinal aberrations of theindividual lenses. This is attributable to the fact that, due to thelenses 1 a ₁ and 1 a ₂ being oppositely controlled, their chromaticlongitudinal aberrations are largely compensated in the zoom system 57 aas a whole.

The zoom system 57 a may replace the zoom systems 57 and 57′ of theconventional microscopy system described with reference to FIG. 4, sothat the microscopy system provides a variable magnification, withoutoptical components having to be mechanically displaced for this purpose.Equally, it is possible to integrate the zoom system 57 a in any otheroptical system, such as, for example, a telescope.

FIG. 6 schematically shows a zoom optics 57 b which comprises thefollowing optical components successively disposed on a common opticalaxis 29 b: lenses 107 ₁ and 109 ₁ which are cemented together and form alens assembly 105 ₁ of positive optical power, a lens 1 b ₁ of variableoptical power, a further lens 1 b ₂ of variable optical power, andlenses 107 ₂ and 109 ₂ which are cemented together and form a lens group105 ₂ of negative optical power. The optical data of the zoom optics 57b regarding materials, radii of curvature and vertex distances areindicated in Table 3 below. In this table, SF1, NSK4, NSK2 and NSF56refer to glass materials which are obtainable from the company SCHOTT,Mainz, Germany:

TABLE 3 Free Radium Thickness diameter Lens No. [mm] [mm] Medium [mm] 164.1383 17.0 107₁ 2.0 SF1 2 34.6203 17.0 109₁ 4.5 NSK4 3 −486.2486 17.00.5 Air  1b₁ 28.8 Air  1b₂ 0.5 Air 4 −130.7438 13.0 107₂ 1.0 NSK2 527.4285 13.0 109₂ 2.5 NSF56 6 46.4366 13.0

Lenses 1 b ₁ and 1 b ₂ of variable optical power are again oppositelycontrollable by a controller (not shown in FIG. 6) for changing animaging ratio of the zoom optics 57 b. The following Table 4 indicatesthe magnifications in three different settings as well as the opticalpowers adjusted for lenses 1 b ₁ and 1 b ₂ to this end. Moreover, thelast three columns of the table indicate the change in the chromaticlongitudinal aberrations of the two lenses 1 b ₁ and 1 b ₂ as a resultof the control as well as the change in the chromatic longitudinalaberration of the zoom optics 57 b as a whole in these settings:

TABLE 4 Index of refraction Chromatic longitudinal [dptr] aberration[dptr] Lens Lens Lens Lens System Setting Magnification 1b₁ 1b₂ 1b₁ 1b₂57b 1 1.6 0 0 0 0 0 2 2.0 4.5 −11.7 −0.5 0.4 −0.1 3 1.3 −4.5 7.8 0.2−0.3 −0.1

Again, it is inferable from this table that the chromatic longitudinalaberration of the lenses 1 b ₁ and 1 b ₂ of variable optical power isrelatively well compensated in the zoom optics 57 b as a whole, due tothese lenses being oppositely controlled.

FIG. 7 schematically shows a further zoom optics 57 c which comprisesthe following components successively disposed along an optical axis 29c: a lens 1 c ₁ of variable optical power, a lens 107 c ₁ and a lens 109c ₁ which are cemented together to form a lens assembly 109 c ₁ of fixedpositive optical power, a lens 107 c ₂ and a lens 109 c ₂ which arecemented together to form a lens assembly 105 c ₂ of fixed negativeoptical power, and a lens 1 c ₂ of variable optical power. The twolenses 1 c ₁ and 1 c ₂ of variable optical power are again oppositelycontrollable by a controller (not sown in FIG. 7) to change amagnification of the zoom optics 57 c. The following Table 5 indicatesthe optical data of the zoom optics 57 c. The lens assemblies of fixedoptical power are identical with the lens assemblies indicated in FIG. 6and Table 3, respectively.

TABLE 5 Free Radius Thickness Diameter Lens No. [mm] [mm] Medium [mm] 1c₁ 2.0 Air 1 64.1383 17.0 107c₁ 2.0 SF1 2 34.6203 17.0 109c₁ 4.5 NSK43 −486.2486 17.0 34.0 Air 4 −130.7438 13.0 107c₂ 1.0 NSK2 5 27.4285 13.0109c₂ 2.5 NSF56 6 46.4366 13.0 2.0 Air  1c₂

Similar to Table 4 relating to the embodiment of FIG. 6, the Table 6below indicates again for the three magnetization settings therespectively adjusted optical powers of the lenses 1 c ₁ and 1 c ₂ ofvariable optical power as well as the changes in the chromaticlongitudinal aberration of these two lenses dependent on the control,and it is indicated how said aberration is compensated in the zoomoptics 57 c as a whole:

TABLE 6 Index of refraction Chromatic longitudinal [dptr] aberration[dptr] Lens Lens Lens Lens System Setting Magnification 1c₁ 1c₂ 1c₁ 1c₂57c 1 1.6 0 0 0 0 0 2 2.0 2.7 −8.6 −0.4 0.3 −0.1 3 1.3 −2.7 5.7 0.2 −0.2−0.0

It is evident from Table 6 that the chromatic longitudinal aberrationsin the optics 57 c as a whole are relatively well compensated due tolenses 1 c ₁ and 1 c ₂ being oppositely controlled. A comparison ofTable 6 with Table 4 shows that, in order to produce the samemagnification 1.6×, 2.0× and 1.3×, smaller changes in the optical powersof the lenses 1 c ₁ and 1 c ₂ are necessary in the zoom optics 57 c thanin the embodiment described with reference to FIG. 6. This is due to thefact that the distance between the lenses 1 c ₁ and 1 c ₂ of variableoptical power of the system 57 c is greater than the distance betweenthe lenses of variable optical power in the embodiment according to FIG.6.

The embodiments of the zoomable imaging optics described with referenceto FIGS. 6 and 7 operate according to the principle of a Galileantelescope, in that a lens group of positive optical power is combinedwith a lens group of negative optical power.

FIG. 8 shows schematically a zoomable imaging optics 57 d which operatesaccording to the principle of a Keplerian telescope, in that two lensgroups of positive optical power are combined, an intermediate imagebeing generated between said two lens groups.

The optics 57 d comprises the following components disposed along acommon optical axis 29 d: a lens 1 d ₁ of variable optical power, lenses107 d ₁ and 109 d ₁ which are cemented together to form a lens assembly105 d ₁ of fixed positive optical power, lenses 107 d ₂ and 109 d ₂which are cemented together to form a lens assembly 105 d ₂ of fixedpositive optical power, and a lens 1 d ₂ of variable optical power.Again, a controller (not shown in FIG. 8) is provided for oppositelycontrolling the lenses 1 d ₁ and 1 d ₂ of variable optical power tochange an imaging ratio and a magnification of the optics 57 d,respectively.

The following Table 7 indicates the optical data of the zoom optics 57d:

TABLE 7 Radius Thickness Free diameter Lens No. [mm] [mm] Medium [mm]Pupil 4.5 30.6 Air  1d₁ 10.0 0.5 Air 1 30.9734 10.0 107d₁ 3.0 NSSK8 2−13.5988 10.0 109d₁ 1.0 SF4 3 −38.0658 10.0 65.5 Air 4 38.0658 10.0107d₂ 1.0 SF4 5 13.5988 10.0 109d₂ 3.0 NSSK8 6 −30.9734 10.0 0.5  1d₂10.0 30.6 Air Pupil 4.5

The following Table 8 indicates for three different settings of themagnification of the zoom optics 57 d the optical powers of lenses 1 d ₁and 1 d ₂, the change in the chromatic longitudinal aberration dependenton the control and how this chromatic longitudinal aberration iscompensated in the zoom optics 57 d as a whole:

TABLE 8 Refractive Chromatic longitudinal index aberration [dptr] [dptr]Lens Lens Lens Lens System Setting Magnification 1d₁ 1d₂ 1d₁ 1d₂ 57d 11.0 0 0 0 0 0 2 1.3 −3.9 5.1 0.2 −0.2 −0.0 3 0.75 5.1 −3.9 −0.1 0.1 −0.0

It is evident from Table 8 that, due to the lenses of variable opticalpower being oppositely controlled, a nearly ideal compensation of thechromatic longitudinal aberration caused by the individual lenses isachieved.

FIG. 9 shows schematically a zoomable imaging optics 43 e for use, forexample, as objective in the microscopy system described with referenceto FIG. 4. The objective 43 e comprises the following optical componentssuccessively disposed along an optical axis 29 e: a lens assembly 105 e₁ of positive optical power consisting of two lenses 107 e ₁ and 108 e ₁cemented together and a lens 109 e ₁, a lens 1 e ₁ of variable opticalpower, a further lens 1 e ₂ of variable optical power and a lensassembly 105 e ₂ of negative optical power consisting of lenses 107 e ₂and 109 e ₂. The two lenses 1 e ₁, 1 e ₂ of variable optical power maybe of the type as described with reference to FIGS. 1 and 2 or of thetype as described with reference to FIG. 3 or of any other lens typecapable of providing a variable optical power. In the embodimentdescribed with reference to FIG. 9, the use of the lens of variableoptical power of the liquid crystal type (FIGS. 1, 2) is, however,preferred, because such lenses can be disposed with ease on the planarlens surfaces of lenses 109 e ₁ and 107 e ₂, respectively. Lenses 1 e ₁and 1 e ₂ are again controlled by a controller (not shown in FIG. 9) forproviding an adjustable optical power. Being provided as liquid crystaltype lenses, lenses 1 e ₁ and 1 e ₂ have a thickness which is small andconstant over its cross-section. The lenses shown in FIG. 9 aresymbolized as glass lenses for a specific adjustment of their opticalpower and provide an optical power corresponding to the individualsetting. It is thus evident that the lens 1 e ₁ in the setting shown inFIG. 9 provides a negative optical power and lens 1 e ₂ provides apositive optical power.

Optical data of the zoomable microscope objective 43 e are indicated inTable 9:

TABLE 9 Radium Thickness Free diameter Lens No. [mm] [mm] Medium [mm] 1150.9268 25.0 107e₁ 4.0 NPSK53 2 −75.6887 25.0 108e₁ 3.0 SF56A 3−383.8371 25.0 0.1 Air 4 99.6563 25.0 109e₁ 3.0 NLAK8 5 Planar 25.0 0.5Air  1e₁ 25.0 14.0 Air  1e₂ 25.0 0.5 Air 6 Planar 25.0 107e₂ 3.0 NSSK8 731.3879 24.0 109e₂ 3.0 NSF6 8 49.2703 23.0 200.0 . . . 300.0  45e Objectplane

The objective 43 e transforms an object-side beam bundle 47 e, emanatingfrom an object plane 45 e, into an image-side beam bundle 49 e having anafocal beam path. By controlling the lenses 1 e ₁ and 1 e ₂, it ispossible to change both a working distance AA between the object plane45 e and the front lens 109 e ₂ and the magnification generated by theobjective 43 e and the focal length thereof, respectively. In order tochange the magnetization, at a given and held working distance AA,lenses 1 d ₁ and 1 e ₂ are oppositely controlled by the controller, thatis, the optical power of one lens is increased and the optical power ofthe other lens is decreased.

The following Table 10 indicates six different settings of the controlof lenses 1 e ₁ and 1 e ₂ for producing three different magnificationsfor each one of two different working distances:

TABLE 10 Working Focal Lens e₁ Lens e₂ distance AA length f 1/f₁ 1/f₂[mm] [mm] [dptr] [dptr] 200 240 −8.7 10.8 200 275 0 0 200 300 5.0 −7.8300 340 −12.1 13.0 300 385 −3.7 3.6 300 430 2.9 −5.8

FIG. 10 shows a zoom optics 57 f which, in the shown setting, comprisesthe following optical components disposed along an optical axis 29 f: alens 1 f ₁ of variable optical power, a lens assembly 105 f ₁ ofpositive optical power consisting of lenses 107 f ₁ and 109 f ₁ whichare cemented together, a lens assembly 105 f ₂ of negative optical powerconsisting of lenses 107 f ₂ and 109 f ₂ which are cemented together,and a lens 1 f ₂ of variable optical power. The lens assemblies 105 f ₁and 105 f ₂ are mounted on a support 115 which is rotatable, like aturret, about an axis 113 oriented transversely to the optical axis 29f. The lens assemblies 105 f ₁ and 105 f ₂ are mounted on the support115 on a common optical axis 111 which, in the setting shown in FIG. 10,coincides with the common axis 29 f of lenses 1 f ₁ and 1 f ₂ ofvariable optical power.

Lenses 1 f ₁, 1 f ₂ are oppositely controllable by a controller (notshown in FIG. 10) for varying a magnification and imaging ratio of theoptics 57 f, respectively. If the lenses 1 f ₁ and 1 f ₂ are controlledsuch that they provide an optical power of Zero, the optics 57 f has abasic magnification of 0.4× in the setting shown in FIG. 10.

Two further lens assemblies 105 f ₁′ and 105 f ₂′ are mounted on thesupport 115, said lens assemblies having a common optical axis 111′enclosing an angle of 60° with the optical axis 111 of the lensassemblies 105 f ₁ and 105 f ₂. When the support 115 is rotatedcounter-clockwise by 60°, the lens assemblies 105 f ₁ and 105 f ₂ areremoved from the beam path between the lenses 1 f ₁ and 1 f ₂ and thelens assemblies 105 f ₁′ and 105 f ₂′ are placed into the beam pathbetween the lenses 1 f ₁ and 1 f ₂ such that the optical axis 111′thereof coincides with the axis 29 f. In this case, when the lenses 1 f₁ and 1 f ₂ are controlled such that they provide no optical power, theoptics 57 f provides a basic magnification of 0.6×.

When the support 105 is further rotated counter-clockwise, the lensassemblies 105 f ₁′ and 105 f ₂′ are removed from the beam path betweenthe lenses 1 f ₁ and 1 f ₂ and the beam path extends through openings117 of the support 115 without a lens of fixed optical power beingdisposed in the beam path between the lenses 1 f ₁ and 1 f ₂. In thiscase, when the lenses 1 f ₁ and 1 f ₂ are controlled to provide nooptical power, the optics 57 f provides a basic magnification of 1.0×.When the support 115 is then further rotated counter-clockwise, the lensassemblies 105 f ₁ and 105 f ₂ are again placed into the beam pathbetween the lenses 1 f ₁ and 1 f ₂. However, the lens assembly 105 f ₂is then at the top in FIG. 10 and the lens assembly 105 f ₁ at thebottom so that, when the lenses 1 f ₁ and 1 f ₂ are not controlled, theoptics 57 f provides a basic magnification of 2.5×. If the support 115is further rotated counter-clockwise by 60°, the optics then provides amagnification of 1.6× when the lenses 1 f ₁ and 1 f ₂ are notcontrolled.

In each one of the above-described settings of the support 115, it ispossible to oppositely control the lenses 1 f ₁ and 1 f ₂ in respect oftheir optical powers in order to vary the magnification provided by theoptics 57 substantially continuously starting out from the basicmagnification adjusted in each case. As the variation of the opticalpowers of lenses 1 f ₁ and 1 f ₂ is limited, the support 115 may then berotated for a further variation of the magnification in order to provideanother basic magnification by the lenses of fixed focal length.

The zoom optics 57 f can be integrated into the microscopy systemdescribed with reference to FIG. 4 for providing in this simple way acontinuous change in the magnification over a relatively wide range,without components of the zoom system having to be displaced inlongitudinal direction relative to the optical axis.

FIG. 11 shows schematically a further zoomable imaging system 57 g,comprising two lenses 1 g ₁ and 1 g ₂ of variable optical power andexhibiting an optical action similar to the embodiment described withreference to FIG. 5. However, a Schmidt-Pechan prism 121 is insertedinto the beam path between the two lenses of variable optical power forfolding the beam path plural times so that an overall length b of theoptics is about 22 mm. Without folding the beam path, the overall lengthwould be 40 mm when use is made of otherwise identical opticalcomponents. Apart from the use of the Schmidt-Pechan prism 121 forfolding the beam path, also other possibilities of deflecting the beamare applicable, such as the use of mirrors, other prism types, such as aPorro-II-prism and the like. By providing a suitable beam folding, it isalso possible to achieve a lateral reversal, if desired.

The above-described principles of the imaging optics of variablemagnification provides a particularly efficient possibility to provide aproduct family with two groups of optical devices which differ from eachother in that the devices of one group exhibit a zoom function and thedevices of the other group do not exhibit a zoom function. The devicesof both groups include optical components of fixed focal length whichare substantially similar in structure. For example, the radii ofcurvature, the free diameters and vertex distances of a majority of theoptical components of fixed focal length of the corresponding devices ofboth groups are substantially similar to each other. The devices of thezoomable group then comprise, as against the devices of the other group,at least two lenses of variable optical power which are inserted in thebeam path spaced apart from one another. This enables to employ a commonmanufacturing process for the corresponding devices of both groups,which allows to provide the product group cost-efficiently.

For example, it is possible to employ the objective described withreference to FIG. 9 in a high-price microscope which provides a zoomfunction, as well as in a low-price microscope which does not providethis function, i.e., not to incorporate the lenses 1 e ₁ and 1 e ₂, butotherwise to maintain the other lenses 107 e ₁, 108 e ₁, 109 e ₁, 107 e₂ and 109 e ₂ substantially unchanged.

Equally, it is possible to use the zoom systems described with referenceto FIGS. 6, 7 and 10 together with the lenses of variable optical powerin a group of microscopes in a model group and to integrate in anothergroup of models substantially the same zoom optics but which do notinclude the lenses of variable optical power, but are otherwise ofsubstantially identical structure.

As is commonly known, spherical lenses whose thickness d on its opticalaxis accounts for much less than the difference of the radial r₁ and r₂of its two surfaces can approximately be referred to as “thin lenses”whose optical power φ_(DL) and dispersion η_(DL) is directlyproportional to the difference of the inverse radii, i.e., thecurvatures k₁ and k₂ of their two surfaces. For assemblies of two ofsuch thin lenses the following applies, likewise in approximation: theoptical power φ of such an assembly is given by the sum of the opticalpowers φ_(a) and φ_(b) of the individual lenses, minus the product ofthe individual optical powers and the lens distance e:φ≅φ_(a)+φ_(b) −e·φ _(a)·φ_(b)  (1)

The dispersion η of such an assembly of two thin lenses is then given inapproximation by the following equation:η≅η_(a)+η_(b) −e·(η_(a)·φ_(b)+η_(b)·φ_(a))  (2)

Let's consider a system of four thin lenses which are disposed in pairswithout a distance therebetween, one of the optical powers of thecomponents of both pairs being fixed (φ_(a,b) ^(f)) and the other onevariable (φ_(a,b) ^(v)). This results into a total optical power (ebeing the distance of the pairs) of:φ≅(φ_(a) ^(f)+φ_(a) ^(v))+(φ_(b) ^(f)+φ_(b) ^(v))−e·(φ_(a) ^(f)+φ_(a)^(v))·(φ_(b) ^(f)+φ_(b) ^(v))  (3),and correspondingly a total dispersion of:η≅(η_(a) ^(f)+η_(a) ^(v))+(η_(b) ^(f)+η_(b) ^(v))−e·[(η_(a) ^(f)+η_(a)^(v))·(φ_(b) ^(f)+φ_(b) ^(v))+(η_(b) ^(f)+η_(b) ^(v))·(φ_(a) ^(f)+φ_(a)^(v))]  (4)

Of particular importance is a simplified equation, in whose derivationit is presumed that the components of fixed focal lengths are configuredsuch that their dispersion is negligible as compared to the dispersionof the components of variable optical power, i.e.:η≅η_(a) ^(v)+η_(b) ^(v) −e·[η _(a) ^(v)·(φ_(b) ^(f)+φ_(b) ^(v))+η_(b)^(v)·(φ_(a) ^(f)+φ_(a) ^(v))]  (5)

A further simplification is achievable for afocal systems, because inthese systems the distance e of the lens pairs must be equal to the sumof the inverse optical powers:η≅η_(a) ^(v)+η_(b) ^(v)−[1/(φ_(b) ^(f)+φ_(b) ^(v))+1/(φ_(a) ^(f)+φ_(a)^(v))]·[η_(a) ^(v)·(φ_(b) ^(f)+φ_(b) ^(v))+η_(b) ^(v)·(φ_(a) ^(f)+φ_(a)^(v))]≅−η_(a) ^(v)·(φ_(b) ^(f)+φ_(b) ^(v))/(φ_(a) ^(f)+φ_(a) ^(v))−η_(b)^(v)·(φ_(a) ^(f)+φ_(a) ^(v))/(φ_(b) ^(f)+φ_(b) ^(v))]≅−η_(a) ^(v)·φ_(b)/φ_(a)−η_(b) ^(v)·φ_(a)/φ_(b)  (6)

It is inferable from this equation that a compensation of the totaldispersion is achievable in an afocal system if the dispersion η_(a)^(v) and η_(b) ^(v) of the lenses of variable optical power anddispersion bear a ratio to each other which is determined by the squaredratio of the optical powers φ_(a) and φ_(b), i.e., by the square of theimaging ratio Γ², and only if η_(a) ^(v) and η_(b) ^(v) have differentpreceding signs. Usually the latter case will occur if both lenses ofvariable optical power are oppositely controlled, i.e., if their opticalpowers φ_(a) ^(v) and φ_(b) ^(v) have also different preceding signs.The variable optical powers to be set are given in an afocal system bythe basic imaging ratio Γ₀ and the imaging ratio Γ to be adjusted ineach case. Therefore, it is generally not possible or not practicable toachieve an exact compensation of the dispersion for all adjustableimaging ratios. It often suffices to provide such an exact compensation,except for the case that the lenses of variable optical powers are notcontrolled at all and thus do not provide any dispersion so that thesystem provides a basic imaging ration, for one further imaging ratio.It is found that, dependent upon the imaging ratio set, the residualdispersion describes a parabolic-type function which, provided thatcolor-corrected components of fixed focal length are provided,intersects zero (corresponding to the negligible dispersion at the basicimaging ratio) and reaches relatively high positive values particularlyfor very large and very small imaging ratios. The vertex of theparabolic-type curve is near the basic imaging ratio if the opticalpower dispersion relations (Abbe values) of the two lenses of variableoptical power are very similar, and are the more remote from the basicimaging ratio, and shifted towards negative dispersion, the more theAbbe values of the lenses differ from each other. By “negativedispersion” it is meant in the present context that the total opticalpower for blue light is less than for red light; if, therefore, anafocal system allowed a polychromatic beam bundle which enters thesystem in parallel to exit in parallel in respect of its green spectralportion, a blue spectral portion would exit the system divergently incase of a negative dispersion and a red spectral portion convergently.In a system with a finite intersection length, a “negative dispersion”means that the intersection length for blue light would be greater thanthe intersection length for red light.

The above derivation also comprises the case that the two components offixed focal length have no optical power at all or are not present atall in that Zero is inserted for the respective optical powers anddispersions. It follows for this special case that an optimum dispersioncompensation is achieved when the image ratio set corresponds to theratio of the Abbe values of the lenses of variable optical power. Ifoptically effective components of fixed focal length are present, anoptimum dispersion compensation is achieved in similar way if the ratiowhich the imaging ratio set bears to the basic imaging ratio correspondsto the ratio of the Abbe values of the lenses of variable optical power.Between this imaging ratio given by said relationship and the basicimaging ratio, the residual dispersion is generally negative and variesonly little with the adjusted imaging ratio set.

Actually, systems of variable optical power cannot exactly be consideredas spaceless, so that every system comprising such lenses must beexactly calculated; the exact conditions for a minimum total dispersionof an imaging system with variable optical power differ in theindividual case also for this reason more or less from the above-derivedgeneral regularities. Other reasons are a neglection of furthersubstantial aberrations and the different demands made on the residualdispersion which is maximally tolerable for the individual application.

The above-discussed lenses of variable optical power may of course besubstituted for by lens systems which each include a plurality of suchlenses or which are composed of several ones of such lenses in order toachieve an even better dispersion compensation. For example, twodifferent lenses which are oppositely controlled may be disposed closelyone behind the other so that together they provide a considerableoptical power, but only a little dispersion; the Abbe value of such acombination would thus be very high. With lenses of the type describedwith reference to FIG. 3 two individual lenses are integrated to athree-layer structure for this purpose, which structure includes(optionally salt) water in the middle and different oils on both sidesthereof. Such a structure can be controlled such that both interfacesshift into the same direction without ever contacting each other.Different lenses of the type according to FIG. 1 can be placed directlyon top of each other and oppositely controlled; moreover, lenses of thetype according to FIG. 1 can be placed directly on one or both glasscovers of lenses of the type according to FIG. 3. These glass covers canalso be replaced by ones providing a fixed optical power in that atleast one of its surfaces is curved and may, in turn, bedispersion-compensated in pairs.

The only independently variable optical parameter of the lenses of thetype shown in FIG. 3 is the curvature k of the interface between the twomedia (water and oil) which per se are invariable. The optical power ofthis interface and the dispersion resulting therefrom are directlyproportional to one another, so that an Abbe value which issubstantially independent of the optical power can be allocated to suchlenses as the ratio of adjusted optical power to the dispersiongenerated thereby. If two of such lenses are integrated in a structure,there must always remain a distance between the two interfaces in orderfor the latter to be preserved at all as areas which are traversedtransversely by the optimal axis, because, if the interfaces contactedone another, a water torus surrounding an oil column would form. What ismore is that this distance varies with the generated optical power in amanner which is dependent on the inner structure of the lenses, becausethe oil and water volumes remain constant, except for theelectrostriction effects. Moreover, such lenses, due to the small radiidifferences and the relatively large lens thicknesses, cannot becalculated exactly as thin lenses. For this reason, it is apparent thata mere approximated calculation of the lens properties is practicallynot sufficient, and much rather an exact calculation is required.Nevertheless, for the purpose of illustration, an approximatedcalculation for thin lenses without distance is performed for anintegrated structure which comprises a normal dispersive immersion oilon one side and a hardly dispersive immersion oil on the other side,with water in-between. The relevant optical parameters of the threemedia used are indicated in Table 11. The adjusted radii for threesettings (including an optically neutral Zero setting) as well as theresulting optical powers and dispersions are indicated in Table 12:

TABLE 11 Medium Refractive index n_(e) Abbe value ν_(e) Water 1.334755.8 Immersion oil Type A 1.4811 56.6 Immersion oil Type B 1.5178 43.0

TABLE 12 Zero setting Setting I Setting II R(A/H₂O) ~∞ +36 mm −12 mmR(H₂O/B) ~∞ +90 mm −30 mm φ(A/H₂O) ~0 −4.1 D +12.2 D φ(H₂O/B) ~0 +2.1 D−6.1 D Optical power φ ~0 −2.0 D +6.1 D η(A/H₂O) ~0 −0.07 D +0.21 Dη(H₂O/B) ~0 +0.06 D −0.20 D Dispersion η ~0 ~0.0 D ~0.0 D

As is evident from Tables 11 and 12, integrated lens systems of thistype are preferably controlled such that the two interface curvaturesbear a constant ratio to one another such that the displacement of thevertexes is always effected in the same direction. This requires anopposite change in the respective contact angle, i.e., also an oppositecontrol. It is then achievable that the effective Abbe value of such asystem remains largely independent of the optical power of the system.In this case, the above-indicated equation (6) is applicable again,according to which the total dispersion is dependent only on theindividual dispersion and the adjusted optical powers of the components.Due to the chromatic aberration being in part already pre-compensated inthe integrated systems, however, the effective Abbe values are in thiscase much higher than in case of an opposite curvature and can also havea negative preceding sign so that the resulting total dispersion can inthe ideal case be kept tolerably small over the entire range of theenvisaged imaging ratio.

FIG. 12 shows schematically an integrated lens combination, the controlof which corresponds approximately to the setting I of Table 12. Thecontroller 13 h controls both the annular electrode 36 h and the twoconical electrodes 35 h separately. The media 26 h and 27 h are oils Aand B of Table 11. The interfaces 33 h, 33 h′ of the water layer 25 hbetween the oils A and B exhibit control-dependent contact angles θ_(A)and θ_(B), respectively. The glass covers 23 h have a thickness of, forexample, 0.55 mm.

In analogy to the zoom system shown in FIG. 5 which comprises two lensesof variable optical power of the type according to FIG. 3, the followingTable 13 indicates the interface radii, optical powers and dispersionsof a similar zoom system consisting of two different lenses, the firstlens including an immersion oil of the type A and the second lens, beingspaced apart by a distance of e=55 mm, including an immersion oil of thetype B:

TABLE 13 Zero setting setting R(H₂O/A) ~∞ +16 mm R(H₂O/B) ~∞ −10 mmφ(H₂O/A) ~0 +9.2 D φ(H₂O/B) ~0 −18.3 D Optical power φ ~0 ~0 D η(H₂O/A)~0 +0.16 D η(H₂O/B) ~0 −0.60 D Dispersion η ~0 ~0.0 D Imaging ratio Γ  1~2

Lens assemblies of the integrated type, even if they per se do not fullycompensate the chromatic aberration, can also be combined to a zoom ofthe type shown in FIG. 5. This allows to make additional variationparameters available in order to compensate the chromatic and further(e.g., spherical) aberrations. Moreover, such combinations allow tostill further compensate the total chromatic aberration in thatintegrated lens systems with such residual aberrations are combinedwhich optimally compensate themselves for a specific imaging ratio.

FIG. 13 shows a combination of two of such integrated lens systemsdisposed on a common optical axis 29 i in an afocal system of theGalilean type. The lens systems are controlled in that the sum of theirfocal lengths, i.e., here the difference of their focal lengths, isabout equal to the distance d_(i) of the lens systems, so that the totaloptical power of the combination of the two lens systems is just Zero.To this end, the control 13 i controls the two annular electrodes 36 iand all four conical electrodes 35 i separately.

If, however, the conical electrodes of an integrated lens system aresynchronously controlled so that the displacement of the vertexes iseffected oppositely, the pre-compensation of the chromatic aberration ηis not that good, but the optical power φ is significantly higher (seeTable 14). Due to the higher optical power of these lens systems, theoverall length is relatively short. Therefore, such systems are suitedbetter for afocal systems of the Keplerian type, as outlined in FIG. 14.In this case, too, the lens systems are controlled such that the sum oftheir focal lengths is about equal to their distance d_(j). Thecompensation of the chromatic aberration can be effected by anappropriate selection of the media of the two integrated systems, atleast for a (here negative) nominal imaging ratio Γ₀, and/or, ifrequired, by means of further lenses of fixed focal length on the commonoptical axis 29 j. As the sum of the individual focal lengths f₁ and f₂shall be constant, the focal length of the other lens system is reducedwhen the focal length of one lens system is increased. This means, thatthe two lens systems are oppositely controlled in order to maintain theafocality of the combination; this, again, results into an at leastpartial compensation of the chromatic aberration.

TABLE 14 Zero setting Setting I Setting II R(A/H₂O) ~∞ ±36 mm ∓12 mmR(H₂O/B) ~∞ ∓90 mm ±30 mm φ(A/H₂O) ~0 ∓4.1 D ±12.2 D φ(H₂O/B) ~0 ∓2.1 D±6.1 D Optical power φ ~0 ∓6.1 D ±18.3 D η(A/H₂O) ~0 ∓0.07 D ±0.21 Dη(H₂O/B) ~0 ∓0.07 D ±0.20 D Dispersion η ~0 ∓0.14 D ±0.41 D Abbe valueNot determined ~44 ~45

In the objective system shown in FIG. 9, the distance between the lensesof positive and negative optical power is so large, or the negativeoptical power is so small as compared to the positive optical power,that, in total, a positive optical power results: It is evident from thesecond line of Table 10 that, when the lenses of variable optical powerare not controlled, the focal length f of this objective is 275 mm andthe working distance AA is 200 mm. As described above, by oppositelycontrolling the lenses of variable optical power, the lens assemblies ofpositive and negative optical power can be influenced such that otherfocal lengths and/or working distances are obtained. According to whathas been described above with reference to equations (1) to (5), thedispersion of the lenses of variable optical power then also changes,and thus the total dispersion. As the distance between the lensassemblies is not defined in any further detail, it is in this case notpossible anymore to indicate a specific optimal ratio of the individualdispersions; rather, this ratio lies in one of two ranges which aredescribed below:

If the lenses of variable optical power are controlled such that thelens disposed rearwardly in the beam path has a positive optical powerand the lens disposed in the front in the beam path has a negative, butin absolute terms a considerably higher optical power, the two lenses ofvariable optical power, due to their small distance as compared to thedifference of their inverse optical powers, have the combined action ofa component having a negative optical power (Equation 1). However, incorrespondence with a relatively long objective focal length, thedistance of the lens assemblies (see above) is larger than itcorresponds to an afocal system, the optimal dispersion ratio regardingthe chromatic aberration compensation must lie beyond the optimum valuefor an afocal system (η_(a) ^(v) _(opt)·φ_(b)/φ_(a)=−η_(b) ^(v)_(opt)·φ_(a)/φ_(b), see Equation 6):e>1/φ_(a)+1/φ_(b)

e>0  (7a)φ>φ_(a)+φ_(b)

φ>0 (because e·φ _(a)·φ_(b)<0)  (7b)|η_(a) ^(v)/η_(b) ^(v)|_(opt)>(φ_(a)/φ_(b))² (wherein|φ_(a)|>|φ_(b)|)  (7c)

However, with simple lenses of variable optical power of the samestructure only. |η_(a) ^(v)/η_(b) ^(v)|_(opt)≈|φ_(a)/φ_(b)| isachievable. Therefore, the lenses of variable optical power should insuch a case be composed differently or/and composed such that the aboveinequality is fulfilled.

If the lenses of variable optical power are controlled such that thelens disposed rearwardly in the beam path has a negative optical powerand the front lens in the beam path has a positive, but in absoluteterms, a higher optical power, the two lenses of variable optical powerhave the combined action, independent of their distance, of an elementof positive optical power (see Equation 1) in correspondence with arelatively short objective focal length. As, in this case, the positiveoptical power of the lens assembly which is closer to the object alreadyexceeds the negative contribution of the lens assembly which is moreremote from the object and the distance-dependent term is likewisepositive, an optimal chromatic aberration correction is again notachievable with simple lenses of variable optical power of the samestructure (see Equation 2 with two positive terms becauseη_(a)+η_(b)>0). One possibility to compensate for chromatic aberrationsconsist in the selection of a higher dispersive lens of variable opticalpower for the lens assembly disposed more remote from the object and alow dispersive lens of variable optical power for lens assembliesdisposed closer to the object. What is meant by high and low dispersivein the present case is that the dispersion is smaller and higher,respectively, at the same optical power, i.e., an effective Abbe valuewould be smaller and higher, respectively. Again, it is not possible toachieve a complete chromatic aberration compensation over the entireworking distance and focal length range; however, except for the casewhere the lenses of variable optical power are not controlled, it ispossible for a still further case, e.g., that of line 5 of Table 10(working distance 300 mm, focal length 385), to obtain a compensation asoptimal as possible, so that at the two working distances an aboutequally well chromatic aberration compensation is provided.

In principle, it is also possible for imaging purposes to use two-stagezoom optics, together with further lenses of fixed focal length, thetotal optical power of said zoom optics being negative in that thedistance between two lens assemblies in said zoom systems is smallerthan it corresponds to an afocal (Galilean) system, provided that theoptical powers of the two lens assemblies have a different precedingsign, or is larger than it corresponds to an afocal (Keplerian) system,provided that the optical powers of the two lens assemblies have thesame, namely positive, preceding sign. Of interest in this respect isparticularly the first case, due to the shorter overall length, in whichcase the distance of the lens assembly is thus between Zero and thedistance for an afocal system having the predetermined optical powers ofthe two lens assemblies (i.e., the sum of the inverse optical powers).Accordingly, the optimum value for the ratio of the individualdispersion lies between the value for a spaceless system (namely η_(a)^(v) _(opt)=−η_(b) ^(v) _(opt); see Equation 2 with e=0) and the optimumvalue for an afocal system (Equation 6):0<e<1/φ_(a)+1/φ_(b)  (8a)0>φ>φ_(a)+φ_(b)  (8b)1<|η_(a) ^(v)/η_(b) ^(v)|_(opt)<(φ_(a)/φ_(b))² (wherein|φ_(a)|>|φ_(b)|)  (8c)

This applies, for example, to a case wherein an integrated system of thetype shown in FIG. 12 consisting of two lenses of the type shown in FIG.3 is controlled such that the difference in the values of the individualinverse optical powers exceeds the, as mentioned, unavoidable distanceof the interfaces and the negative optical power of the one interface ishigher in value than the positive optical power of the other interface.An optimum control of such a system preferably takes account of theinterface distance which changes with the adjusted optical power.

Moreover, in these lens systems the dispersion is at least approximatelyproportional to the optical power, so that in each case an effectiveAbbe value ν=φ/η can be indicated which is even largely independent ofthe adjusted optical power and is determined only by the opticalparameters of the liquids contained in the lens. On this condition, itfollows from Equation 8c the optical value range in respect of thechromatic aberration compensation for the (amount)ratio of these Abbevalues:|φ_(b)/φ_(a)|<|ν_(b)/ν_(a)|_(opt)<φ_(a)/φ_(b)| (wherein|φ_(a)|>|φ_(b)|)  (9a)

For systems with particularly small interface distances or, to be moreexact, principal plane distances, the optimum is nearer to the lowerlimit, i.e.:|φ_(b)/φ_(a)|<|ν_(b)/ν_(a)|_(opt)<1 (wherein |φ_(a)|>|φ_(b)|)  (9b)

Accordingly, for systems with particularly small differences in theoptical power, or larger interface distances, the optimum is thus nearerto the upper limit, i.e.:1<|ν_(b)/ν_(a)|_(opt)<|φ_(a)/φ_(b)| (wherein |φ_(a)|>|φ_(b)|)  (9c)

As in all other above-described examples, the optimum choice for theindividual dispersions and Abbe values, respectively, is also dependenton the further aberrations, particularly spherical aberrations, whichmust also be compensated, and on the residual aberrations which is stilltolerable in the respective application.

In the following, embodiments of the stereo-microscopy system accordingto the invention are described which make use of optical assemblies ofvariable optical action.

In the objective shown in FIG. 15, the lens assembly 63 further includesa lens 66 of variable optical power which is disposed on the side oflens 65 which is not cemented with lens 64. The structure of lens 66 ofvariable optical power corresponds to that described with reference toFIG. 1. To this end, the assembly 1 described with reference to FIG. 1is provided in the form of a flexible film which has a thickness ofabout 100 μm and is fixedly connected to the lens 65 over the entiresurface thereof. However, it is also possible to dispose the lens 66 ofvariable optical power spaced apart from the surface of lens 65, forexample, on a planar glass support.

Equally, it is possible to dispose the lens of variable optical power onthe surface of lens 64 which is not cemented with lens 65.

Optical data of both lenses 64 and 65 regarding materials, radii ofcurvature and vertex distances are indicated in Table 15 below. In thistable, NSSK8 and NSF56 refer to glass materials which are obtainablefrom the company SCHOTT, Mainz, Germany.

TABLE 15 Thickness/ Free Lens Surface Radius Airgap Glass/ diameter No.No. [mm] [mm] Medium [mm] 1 142.549 43.0 65 6.5 NSSK8 2 −105.481 43.0 643.5 NSF56 3 −364.018 200.0 Luft 43.0 Object plane

Accordingly, an overall height of the lens assembly 63 is 10 mm, and afocal length of the two lenses 65 and 64 together is 205 mm, so that thefocal length of the total lens assembly 63 consisting of lenses 64, 65,66 is 205 mm if the lens 66 of variable optical power provides anoptical power of 0 dptr.

FIGS. 15 a, 15 b, 15 c show beam paths of the object-side beam bundle 47k between the object plane 45 k and the objective 43 k for threedifferent settings of the optical power of lens 66 k. Moreover, FIGS. 15a, 15 b, 15 c show for each setting the focal length f of the objective43 k and the working distance A between the object plane 45 k and thelens surface 64 k facing the same.

In the setting of FIG. 15 a, lens 66 k provides an optical power of 0dptr. In the setting of FIG. 15 b, lens 66 k provides an optical powerof −1.6 dptr. FIG. 15 b does not show lens 66 k as layer of constantthickness, but symbolically as a convex lens of glass material whichlikewise provides an optical power of −1.6 dptr. In the setting of FIG.15 c, lens 66 k provides an optical power of −2.4 dptr. Here, too, lens66 k is symbolically represented as glass lens of corresponding opticalpower.

The optical data of the objective 43 k in the three settings shown inFIGS. 15 a to 15 c are summarized in Table 16 below.

TABLE 16 Setting A [mm] f [mm] 1/f [dptr] Δ1/f [dptr] 1 200 205 4.9 0 2300 304 3.3 −1.6 3 400 403 2.5 −2.4

In the following, further variants of the embodiment described withreference to FIGS. 1 to 4 are described, Components which correspond instructure and function to the components of FIGS. 1 to 4 are designatedby the same reference numbers, but, for the purpose of distinction, aresupplemented by an additional letter. In this respect, reference istaken to the entire above description.

FIG. 16 shows a variant of an afocal zoom system 57 l for use in themicroscopy system of FIG. 4. In FIG. 4, the zoom system 57 of variablemagnification is controlled in that two of the four lens groups 58 ofthe zoom system 57 are displaceable along an optical axis 54 of thepartial stereo optics 51. The zoom system 57 l shown in FIG. 16comprises two lens assemblies 58 l ₁ and 58 l ₂ which are disposedspaced apart from each other at a fixed distance along an optical axis54 l of the zoom system 57 l. The lens assembly 58 l ₁ is disposed nearthe objective, not shown in FIG. 16, and the lens assembly 58 l ₂ isdisposed near the tube, likewise not shown in FIG. 16. The lens assembly58 l ₁ comprises a lens of negative optical power 71 ₁ which is cementedtogether with a lens 72 ₂ of positive optical power. A lens 73 ₁ ofvariable optical power is disposed over the entire surface of lens 72 ₁which is not cemented with the lens 71 ₁, in similar manner as it hasalready been described with reference to FIGS. 3 and 4 for the lens 66of the objective 43.

The lens assembly 58 l ₂ comprises a lens 71 ₂ of negative optical powerwhich is cemented with a lens 72 ₂ of positive optical power. A lens 73₂ of variable optical power is likewise disposed over the entire surfaceof the lens 71 ₂ which is not cemented with the lens 71 ₂. The lenses 73₁ and 73 ₂ of variable optical power are controlled by a controller 13 lfor controlling their optical powers to change the magnification of thezoom system 57 l.

FIGS. 16 a, 16 b, and 16 c show three different settings of the zoomsystem 57 l for three different magnifications. Here, too, the lenses 73₁ and 73 ₂ are not shown as layers of constant thickness, but ascorresponding lenses of glass which provide an optical power accordingto the respective setting.

The optical data of lenses 71 ₁, 72 ₁, 71 ₂ and 72 ₂ regardingmaterials, radii of curvature and vertex distances are indicated inTable 17 below. In said table, SF1, NSK4, NSK2 and NSF56, again, referto glass materials which are obtainable from the company SCHOTT, Mainz,Germany.

TABLE 17 Thickness/ Free Lens Surface Radius Airgap Glass/ diameter No.No. [mm] [mm] Medium [mm] 1 64.1383 17.0 711 2.0 SF1 2 34.6203 17.0 7214.5 NSK4 3 −486.249 17.0 34.0 Luft 4 −130.744 13.0 712 1.0 NSK2 527.4285 13.0 722 2.5 NSF56 6 46.4366 13.0

Table 18 below indicates the values for the magnifications provided bythe zoom system 57 l in the three settings according to FIGS. 16 a, 16b, 16 c as well as the respectively set optical powers of lenses 73 ₁and 73 ₂ are indicated.

TABLE 18 1/f (dptr) 1/f (dptr) Setting Magnification Lens 73₁ Lens 73₂ 1(FIG. 5a) 2.0 4.1 −11.2 2 (FIG. 5b) 1.6 0 0 3 (FIG. 5c) 1.3 −4.1 7.5

FIG. 17 shows an ocular 55 m for use in a stereo-microscopy system.

The ocular 55 m comprises a lens assembly 80 consisting of a lens 81 ofnegative optical power which faces the tube of the stereomicroscopysystem and is cemented with a lens 82 of positive optical power, and afurther lens of positive optical power 83 which has applied thereon overits entire surface a lens 84 of variable optical power. The lens 84 ofvariable optical power is controllable by a controller 13 m to changethe optical power of lens 84 thereof in order to compensate a visiondefect of an eye viewing through the ocular 55 m.

FIGS. 17 a, 17 b, 17 c show three different settings of the ocular 55 m,the eye viewing through the ocular 55 m being symbolically representedby an eye pupil AP and a lens 85 which symbolizes the vision defect. InFIG. 17 a the vision defect is +4 dptr and the lens 85 symbolizing thevision defect is shown as plano-convex lens. In FIG. 17 b the visiondefect is 0 dptr, i.e., the eye is of ideal vision, and the lens 85symbolizing the vision defect is shown as plano-parallel plate. In FIG.17 c, the vision defect is −4 dptr and the lens 85 symbolizing thevision defect is accordingly shown as plano-concave lens. Reference signZB indicates in FIGS. 17 a, 17 b and 17 c an intermediate imagegenerated by the tube of the microscopy system.

Optical data of the lenses 81, 82, 83 of the ocular 55 m regardingmaterials, radii of curvature and vertex distances are evident fromTable 19 below. Again, SF56A and SK55 refer to glass materials which areobtainable from the company SCHOTT, Mainz, Germany.

TABLE 19 Thickness/ Free Lens Surface Radius Airgap Glass/ diameter No.Nr. [mm] [mm] Medium [mm] Intermediate image 14.47 1 122.32 28.0 81 4.0SF56A 2 21.288 28.0 82 13.0 SK55 3 −38.681 29.0 0.3 Air 4 24.406 27.5 837.2 SK55 5 Planar 25.2 25.0 Eye pupil

In FIGS. 17 a, 17 b, 17 b, too, lens 84 of variable optical power is notshown as a layer of constant thickness, but as a glass lens which isground such that it provides an optical power corresponding to lens 84.

The controller 13 m comprises a memory 87 for storing thecharacteristics of the three different settings of lens 84 shown inFIGS. 17 a to 17 c. These characteristics are selectively fetched fromthe memory 87 to adjust the lens 84 accordingly. In order to change thesetting, a selection switch 89 is coupled to the control 13 m, whichswitch offers three selectable settings in the depicted embodiment.Accordingly, in the depicted embodiment, the ocular 55 m can thus bequickly switched over in order to compensate a vision defect of +4 dptrof a first user for the latter to optimally perceive the stereoscopicimage, in order to provide a setting for the second user with optimalvision for the latter to optimally perceive the stereoscopic image aswell, and in order to offer a setting for a third user, which settingcompensates a vision defect of −4 dptr. For other or further users, thememory may then contain other characteristics for the respective visiondefects. The stored value can be predetermined by means of an inputmeans, not shown in FIG. 17.

FIG. 18 shows a further variant of the stereo-microscopy systemdescribed with reference to FIGS. 4 and 15 which differs from the latterin the way a lens 66 n of variable optical power is controlled. The lens66 n is not only controlled to change a working distance in that itprovides a variable round lens action in respect of an optical axis 42 nof the objective 63 n, but still provides an additional round lensaction in respect of optical axes 54 n and 54′n of a left-hand partialstereo optics 51 n and a right-hand partial stereo optics 51′n,respectively. Zoom systems 57 n and 57′n of the partial optics 51 n and51′n, respectively, comprise lens assemblies 58 n and 58′n,respectively, which are displaceable along the optical axes 54 n and54′n, respectively, of the partial optics, as this is symbolicallyrepresented by arrows 91 and 91′ in FIG. 7. The displacement of the lensassemblies 58 n, 58′n for changing a magnification provided by the zoomsystems 57 n, 57′n is effected by a controller 13 n which likewisecontrols the lenses 66 n of variable optical power.

The lens 66 n of variable optical power is controlled dependent on theadjusted magnification in order to provide in the respective partialbeam bundle 53 n, 53′n an additional optical power, as it is representedin FIG. 18 by symbolical convex lenses 92 and 92′. As a result, the lens66 n of variable optical power can assume the function of the zoomsystems 57 n, 57′n so that the latter as such can operate with at leastone optical component less than usual.

The zoom systems 57 n, 57′n are displaceable about the optical axis 42 nof the objective 43 n in circumferential direction, as intimated byarrow 93 in FIG. 7. Accordingly, the optical axes 54 n, 54′n aredisplaced in circumferential directional about the optical axis 42 n,and the control 13 controls the lens 66 n continuously such that theadditional lens actions 92, 92′ are provided symmetrically in respect ofthe axes 54 n and 54′n, respectively.

FIG. 19 shows schematically a further stereo-microscopy system 41 o. Incontrast to the above-described stereo-microscopy systems, thestereo-microscopy system 41 o comprises two partial stereo optics 51 oand 51′o, each of which includes a separate objective 63 o and 63′o,respectively, as well as symbolically represented zoom systems 58 o and58′o and, moreover, a tube 59 o and 59′o, respectively, and an ocular 55o and 55′o, respectively. The objective 63 o (63′o), the zoom system 58o (58′o), the tube with field lens 59 o (59′o) and the ocular 55 o(55′o) are disposed symmetrically along the optical axis 54 o (54′o) andfixedly supported in a housing 101 of the stereo-microscopy system suchthat the optical axes 54 o and 54′o enclose an angle α of about 6°, theaxes 54 o, 54′o being disposed symmetrically in respect of principalaxis 42 o of the stereo microscopy system 41 o.

The objectives 63 o and 63′o are identical in structure with a lens 64 o(64′o) of negative optical power, a lens 65 o (65′o) of positive opticalpower and a lens 66 o (66′o) of variable optical power, similar to theobjective of the microscopy system described with reference to FIGS. 4and 15. The optical power of the lens 66 o is variable by means of acontroller, not shown in FIG. 19, for changing a focal length of theobjective 63 o in order to vary a working distance of thestereo-microscopy system 41 o, i.e., a distance between an object plane45 o and the objective 63 o. FIG. 19 shows two settings of the workingdistance with object planes 45 o, and 45 o ₂. However, at a shorterworking distance from the object plane 45 o ₂, precise stereo images canonly be obtained if the optical axes 54 o ₂ and 54′o ₂ extend betweenthe objectives 63 o and 63′o such that they intersect in the objectplane 45 o ₂ on the principal axis 42 o. In order to provide such a“bent” of the optical axes 54 o ₂ and 54′o ₂, the lenses 66 o and 66′oof variable optical power are in addition controlled such that they actas an optical wedge, as symbolically represented by the dashed line inFIG. 19.

FIG. 20 shows a further variant of an afocal zoom system 57 p for use inthe microscopy system of FIG. 4. The zoom system 57 p shown in FIG. 20comprises two lens assemblies 58 p ₁ and 58 p ₂ which are disposedspaced apart from one another by a fixed distance along an optical axis54 p of the zoom system 57 p. The lens assembly 58 p ₁ is disposed closeto the objective, not shown in FIG. 20, and the lens assembly 58 p ₂ isdisposed close to the tube, likewise not shown in FIG. 20. The lensassembly 58 p ₁ comprises a lens 71 p ₁ of negative optical power whichis cemented with a lens 72 p ₁ of positive optical power.

Equally, the lens assembly 58 p ₂ comprises a lens 71 p ₂ of negativeoptical power which is cemented with lens 72 p ₂ of positive opticalpower. The lens assemblies 58 p ₁ and 85 p ₂ are of identical structureand mirror-symmetrical in respect of a plane extending orthogonally tothe optical axis 54 p.

A further lens assembly 97 is disposed between the two lens assemblies58 p ₁ and 58 p ₂, said lens assembly comprising two lenses 94 and 96 ofpositive optical power which are identical in shape and disposedlikewise mirror-symmetrical in respect of a plane disposed between thetwo lenses 94, 96. A lens 95 of negative optical power is interposed inthe space between the two lenses 94 and 96 and cemented with the twolenses 94 and 96. The lens assembly 97 is displaceable along the opticalaxis 54 p by means of a drive 99 to change a magnification the zoomsystem 57 e.

In contrast to the zoom system shown in FIG. 4, wherein two out of fourlens assemblies are displaceable along the optical axis, only lensassembly 97, out of the four lens assemblies 58 p ₁, 58 p ₂, 97 of thezoom system 57 p according to FIG. 20, is displaceable along the opticalaxis 54 p, and the two other lens assemblies 58 p ₁ and 58 p ₂ arefixedly disposed on the optical axis. In order to compensate remainingimage position defects, the zoom system 57 p comprises a lens 73 p ofvariable optical power which, in the embodiment shown in FIG. 20, isdisposed close to the lens 71 p ₁ at a small distance spaced aparttherefrom. Equally, the lens of variable optical power could be disposedon one of the surfaces of the lenses 71 p ₁, 72 p ₁, 72 p ₂ and 71 p ₂,or the lens of variable optical power could also be disposed at anotherposition of the beam path of the zoom system 57 p.

FIGS. 20 a, 20 b, 20 c show three different settings of the zoom system57 p for three different magnifications, the lens 73 p of variableoptical power being not depicted as layer of constant thickness, but asa corresponding glass lens which provides the corresponding opticalpower for the respective setting. The lens 73 p of variable opticalpower and the motor 99 for displacing the lens assembly 97 along theoptical axis 54 p are controlled by a controller 13 p which comprises amemory for storing the control values for the lens 73 p of variableoptical power and the motor 99 for the respective magnification values.

The optical data of lenses 71 p ₁, 72 p ₁, 96, 95, 72 p ₂ regardingmaterials, radii of curvature and vertex distances are evident fromTable 20 below. SF56A, SSK51, SF57, LSFN7, again, refer to glassmaterials which are obtainable from the company SCHOTT.

TABLE 20 Thickness/ Free Lens Surface Radius Airgap Glass/ diameter No.No. [mm] [mm] Medium [mm] 1 31.851 16.0 71e1 1.8 SF56A 2 18.701 16.072e1 3.4 SSK51 3 −325.46 16.0 0.8 . . . 32.7 (d2) 4 −19.527 6.3 96 1.5SF57 5 −8.0006 6.3 95 0.8 LAFN7 6 8.0006 6.3 94 1.5 SF57 7 19.527 6.332.7 . . . 0.8 (d1) 8 325.46 16.0 72e2 3.4 SSK51 9 −18.701 16.0 71e2 1.8SF56A 10 −31.851 16.0

For the settings shown in FIG. 20 a, 20 b, 20 c, the following Table 21indicates the values for the magnification provided by the zoom system57 p and the respective optical powers 1/f and distances d between thelenses adjusted in each case.

TABLE 21 1/f d1 d2 [dptr] e Setting [mm] [mm] Magnification lens 1 (FIG.9a) 0.8 32.7 2.4 0 2 (FIG. 9b) 19.3 14.2 1.0 4.6 3 (FIG. 9c) 32.7 0.80.4 0

In contrast to the conventional zoom systems including two displaceablelens assemblies, the zoom system 57 p shown in FIG. 20 is advantageousin so far as it exhibits a short overall length. Moreover, in order tochange the magnification, only one lens assembly need to be displacedalong the optical axis. Therefore, a complex cam control for displacinglens assemblies, as used in conventional systems, can be dispensed with.This entails a considerable simplification of the mechanics as well asof the adjustment required due to unavoidable mechanical and opticaltolerances of the zoom system. For example, the necessary mechanic imageposition adjustment can simply be completely replaced by correspondinglycontrolling the linear drive.

In summary, objectives are proposed which comprise adjustable opticalelements and, if desired, lenses of fixed focal length. By appropriatelycontrolling the adjustable optical elements, the characteristics of theoptics can thus be advantageously varied. To this end, systems areprovided which are suitable for use as surgical stereo-microscope,objective, ocular and zoom, respectively.

A zoomable imaging optics according to the invention comprises lenses ofvariable optical power which, in order to change a magnification, can beoppositely controlled in the sense that the optical power of one lens isincreased and the optical power of the other lens is decreased. Inaddition, the imaging optics may include further assemblies of fixedfocal length.

While the invention has been described with respect to certain exemplaryembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, the exemplary embodiments of the invention set forth hereinare intended to be illustrative and not limiting in any way. Variouschanges may be made without departing from the spirit and scope of thepresent invention as defined in the following claims.

What is claimed is:
 1. An imaging optics, comprising: a first lens ofvariable optical power; a second lens of variable optical power, whereina common optical axis is assignable to each of the first and secondlenses of variable optical power; and a controller adapted to controlthe first lens of variable optical power in order to increase theoptical power provided by same, and to control the second lens ofvariable optical power in order to decrease the optical power providedby same, or to control the first lens of variable optical power in orderto decrease the optical power provided by same, and to control thesecond lens of variable optical power in order to increase the opticalpower provided by same, for providing an adjustable total refractivepower of the imaging optics different from zero.
 2. The imaging opticsaccording to claim 1, further comprising at least one lens assembly ofat least one lens of fixed optical power, having an optical axis, whichsubstantially coincides with the common optical axis of the first andsecond lens of variable optical power.
 3. The imaging optics accordingto claim 2, wherein the first lens assembly with at least one lens offixed optical power, the first lens of variable optical power, thesecond lens of variable optical power and a second lens assembly with atleast one lens of fixed optical power are arranged along the commonoptical axis in this order.
 4. The imaging optics according to claim 2,wherein the first lens of variable optical power, the first lensassembly with at least one lens of fixed optical power, a second lensassembly with at least one lens of fixed optical power and the secondlens of variable optical power are arranged along the common opticalaxis in this order.
 5. The imaging optics according to claim 1, whereinthe controller controls the first and second lenses such that the firstand second lenses have different signs of optical powers from oneanother when effect of the imaging optics does not satisfy a requiredimaging quality.
 6. The imaging optics according to claim 1, wherein aspace along the common optical axis between the first and the secondlens of variable optical power is free of further lenses of fixedoptical power.
 7. The imaging optics according to claim 1, furthercomprising at least one lens assembly of at least one lens of fixedoptical power, having an optical axis, which substantially coincideswith the common optical axis of the first and second lens of variableoptical power.
 8. The imaging optics according to claim 7, wherein thefirst lens assembly with at least one lens of fixed optical power, thefirst lens of variable optical power, the second lens of variableoptical power and a second lens assembly with at least one lens of fixedoptical power are arranged along the common optical axis in this order.9. The imaging optics according to claim 7, wherein the first lens ofvariable optical power, a first lens assembly with at least one lens offixed optical power, a second lens assembly with at least one lens offixed optical power and the second lens of variable optical power arearranged along the common optical axis in this order.
 10. The imagingoptics according to claim 1, wherein the first lens and the second lensof variable optical power each provide a dispersion variable with therespective optical power, and wherein the dispersions of the first andsecond lens of variable optical power and the controlling of the firstand second lens of variable optical power are adjusted to one anothersuch that the following condition is fulfilled:|η₁+η₂<|η₁|+|η₂|, wherein |η₁+η₂| is a combined dispersion amount of thefirst and second lens of variable optical power, and |₁| and |η₂| areindividual dispersion amounts of the first and second lens of variableoptical power.
 11. The imaging optics according to claim 1, wherein thefirst lens and the second lens of variable optical power each provide adispersion variable with the optical power, and wherein the variabledispersions of the first and second lens of variable optical power andthe controlling of the first and second lens of variable optical powerare adjusted to one another such that the following condition isfulfilled:|η₁+η₂|<Max(|η₁|;|η₂|), wherein |η₁+η₂| is a combined dispersion amountof the first and second lens of variable optical power, |η₁| and |η₂|are individual dispersion amounts of the first and second lens ofvariable optical power, and Max (|η₁|;|η₂|) is a larger one of theindividual dispersion amounts of the first and second lens of variableoptical power.
 12. The imaging optics according to claim 1, wherein atleast one of the first lens and the second lens of variable opticalpower comprises two partial lenses of variable optical power, arrangedin succession in the beam path, and wherein the controller is adapted tocontrol the partial lenses of the at least one of the first and secondlens of the variable optical power.
 13. The imaging optics according toclaim 12, wherein the partial lenses each comprise an interface betweentwo liquid media, and wherein the controller is adapted to control thepartial lenses such that intersection points of the optical axis withthe interfaces of the partial senses are displaced in the samedirection.
 14. The imaging optics according to claim 1, furthercomprising a first partial imaging optics with at least one lens offixed optical power and with a first optical axis, and the secondpartial imaging optics with at least one lens of fixed optical power andwith a second optical axis, wherein the first and second partial imagingoptics are displaceable such that, selectively, the first optical axisor the second optical axis substantially coincides with the commonoptical axis of the first and second lenses of variable optical power.15. The imaging optics according to claim 14, wherein a first imagingratio of the imaging optics at a setting of the optical powers of the atleast two first and second lenses of variable optical power and at anarrangement of the first optical axis on the common optical axis, isdifferent from a second imaging ratio of the imaging optics at thesetting of the optical powers of the at least tow first and secondlenses of variable optical power and at an arrangement of the secondoptical axis on the common optical axis.
 16. The zoomable imaging opticsaccording to claim 15, wherein${{2\frac{{M_{1} - M_{2}}}{\left( {M_{1} + M_{2}} \right)}} > 0},3,\text{wherein}$M₁ is the first imaging ratio and M₂ is the second imaging ratio. 17.The imaging optics according to claim 15, wherein the first and secondpartial imaging optics each comprise a telescope arrangement.
 18. Theimaging optics according to claim 1, further comprising at least onemirror surface arranged along the common optical axis, for folding abeam path of the imaging optics.
 19. the imaging optics according toclaim 18, wherein the at least one mirror surface is arranged betweenthe first lens of variable optical power and the second lens of variableoptical power.
 20. The imaging optics according to claim 15, having atleast one lens of variable optical power, for which: D<Δf·k wherein D isan effective diameter of the at least one lens of variable opticalpower, Δf represents a maximum change of a focal length of the at leastone lens of variable optical power, and k is a constant within the rangeof about 0.9 to about 1.2.
 21. The imaging system according to claim 1,wherein at least one of the first and second lenses of variable opticalpower comprises at least one liquid crystal layer, and optical pathlength of which is spatially dependently adjustable.
 22. The imagingoptics of claim 1, wherein the first and second lens of variable opticalpower are combined into an integrated lens assembly.
 23. The imagingoptics of claim 1, wherein the first lens and the second lens ofvariable optical power each provide at least one kind of opticalaberration variable with the optical power, and wherein the variableoptical aberration of the same king of the first and second lens ofvariable optical power and the controlling of the first and second lensof variable optical power are adjusted to one another such that anabsolute value of a resulting optical aberration of the imaging opticsof the same kind is smaller than a sum of absolute values of the opticalaberrations of the same kind of the first and second lens of variableoptical power.
 24. The imaging optics of claim 1, wherein the first lensand the second lens of variable optical power each provide at least onekind of optical aberration variable with the optical power, and whereinthe variable optical aberration of the same kind of the first and secondlens of variable optical power and the controlling of the first andsecond lens of variable optical power are adjusted to one another suchthat an absolute value of a resulting optical aberration of the imagingoptics of the same kind is smaller than a larger one of absolute valuesof the optical aberrations of the same kind of the first and second lensof variable optical power.
 25. An imaging optics, comprising: a firstlens of variable optical power; a second lens of variable optical power,wherein a common optical axis is assignable to the first and secondlenses of variable optical power; and a controller adapted to controlthe first lens of variable optical power in order to increase theoptical power provided by same, and to control the second lens ofvariable optical power in order to decrease the optical power providedby same, or to control the first lens of variable optical power in orderto decrease the optical power provided by same, and to control thesecond lens of variable optical power in order to increase the opticalpower provided by same, further comprising an arrangement for centeringthe first and second lenses of variable optical power in respect of thecommon optical axis.
 26. The imaging optics of claim 25, wherein saidarrangement for centering the first and second lenses of variableoptical power is symmetrical in respect of the common optical axis, andis in contact with the first and second lenses of variable opticalpower.
 27. The imaging optics of claim 25, wherein said arrangement forcentering the first and second lenses of variable optical powercomprises a conical wall.
 28. The imaging optics of claim 25, providinga total refractive power of the imaging optics adjustable to zero. 29.The imaging optics of claim 25, comprising at least one fluid medium orliquid crystal.
 30. The imaging optics of claim 25, providing adjustabletotal refractive power of the imaging optics different from zero. 31.The imaging optics of claim 25, wherein the first lens and the secondlens of variable optical power each provide at least one kind of opticalaberration variable with the optical power, and wherein the variableoptical aberration of the same kind of the first and second lens ofvariable optical power and the controlling of the first and second lensof variable optical power are adjusted to one another such that anabsolute value of a resulting optical aberration of the imaging opticsof the same kind is smaller than a sum of absolute values of the opticalaberrations of the same kind of the first and second lens of variableoptical power.
 32. The imaging optics of claim 25, wherein the firstlens and the second lens of variable optical power each provide at leastone kind of optical aberration variable with the optical power, andwherein the variable optical aberration of the same kind of the firstand second lens of variable optical power and the controlling of thefirst and second lens of variable optical power are adjusted to oneanother such that an absolute value of a resulting optical aberration ofthe imaging optics of the same kind is smaller than a larger one ofabsolute values of the optical aberrations of the same kind of the firstand second lens of variable optical power.
 33. An imaging optics,comprising: a first lens of variable optical power; a second lens ofvariable optical power, wherein a common optical axis is assignable tothe first and second lenses of variable optical power; and a controlleradapted to control the first lens of variable optical power in order toincrease the optical power provided by same, and to control the secondlens of variable optical power in order to decrease the optical powerprovided by same, or to control the first of variable optical power inorder to decrease the optical power provided by same, and to control thesecond lens of variable optical power in order to increase the opticalpower provided by same, for providing an adjustable total refractivepower of the imaging optics, further comprising at least one totallyreflective surface arranged on the common optical axis for folding abeam path of the imaging optics.
 34. The imaging optics of claim 25,wherein the at least one totally reflective surface is arranged betweenthe first lens of variable optical power and the second lens of variableoptical power.